Non-destructive inspection (NDI) of composite structures assembled with adhesive bonds is a need in, among other industries, the aircraft industry. Among other techniques, laser bond inspection (LBI) has proven useful. Normally, LBI involves deposition of laser energy onto the front surface of a bonded article, generating compression waves that reflect off of the back surface of the bonded article as tensile waves, the tensile waves predominantly providing the stresses that interrogate the bond. However, in a number of tasks, final paste bonds are not easily inspected by conventional LBI. For example, conventional LBI may be impractical in the inspection of aircraft closeout structures because the composite structure to be lased may be at least partially enclosed.
LBI employs stress wave generation principles similar to those used in laser shock processing. Laser shock processing assemblies and methods are described in U.S. Pat. Nos. 5,741,559, 5,911,891, 6,412,331, and 5,131,957, each of which is incorporated by reference herein in its entirety. However, each of these assemblies and methods involves the use of a
tamping fluid over the article to be processed. More particularly, a substantially opaque layer covers the surface of the article to be processed. The substantially opaque layer may be, for example, tape or paint. The substantially opaque layer is then covered by a substantially transparent layer. The substantially transparent layer is typically water. However, as indicated above, many NDI tasks involve, for example, enclosed structures, and, thus, the use of a tamping fluid is not desirable, practical, or possible.